Sound projecting apparatus



May. 9, 1967 G. J. SIELER SOUND PROJECTING APPARATUS 4 Sheets-Sheet 1 Filed April 4, 1962 FIG G. JEROME SIELER INVENTOR.

y ,1967 G.J.S|ELER' Q I 3,319,001

SOUND PROJECTING APPARATUS Filed April 4, 1962 v 4 Sheets-Sheet 2 FIG 2 6o 60 I6 l I M FIG 8 D D l G. JEROME SIELER IN V EN TOR.

ATTORNEY May 9, 1967 G. J. SIELER 3,319,001

SOUND PROJECTING APPARATUS Filed April 4, 1962 4 Sheets-Sheet 5 FIG G. JEROME SIELER ATTORNEY May 9, 1967 G. J. SIELER SOUND PROJECTING APPARATUS v 4 Sheets-Sheet 4 Filed April 4, 1962 FIG G. JEROME SIELER 7 4 lil il G I IIIIITII c w 7 97 L/ @z ATTORNEY United States Patent Filed Apr. 4, 1962, Ser. No. 185,014 7 Claims. (Cl. 179-1) This invention relates to a new and useful concept in a sound projecting device useful in a portable voice projector or lectern and more particularly to a portable, battery-powered, transistorized voice projecting lectern which does not have to be connected by cords or wires to conference room or auditorium electrical systems in order to operate.

Most people are aware of the awkward public address systems which are customarily used in conference rooms and auditoriums. Normally there will be, at least in the case of larger rooms, perhaps several speakers, a separate amplifier and volume control console, and one or more microphones. All of these various pieces of equipment must be connected to each other by use of wires. In addition, a cord must run from the electrical outlet to the amplifier. Inevitably wires will get tangled in the feet of the persons present in the room. As a result connections are lost and the public address system ceases to function. The wiring then must be traced out to find where the break has occurred. Such public address systems are expensive, require time in which to be set up for a particular occasion and also demand time in which to be dismantled. Furthermore, they are bulky and heavy and generally because of their awkwardness are quite ineflicient and inconvenient to use.

Other problems contributing to the inefliciency of conventional systems result largely from design factors. For instance an out of phase relationship between the propagated sound and the source sound, i.e. between speaker cone and microphone, has the effect of cancelling out part of the propagated or projected sound and thus fails to give all of the amplification to the sound which could otherwise be achieved. Another problem springs from the failure of designers to isolate or insulate the speaker cone and/ or horn from the case or cabinet in which it is mounted. The effect of such failure is to invite feedback and hence interference with and distortion of the projected sound. Another significant problem arises with respect to horn design. Certain optimum relationships can be established between various parts of the horn and the failure of hitherto known systems to utilize such relationships can be ascertained in inefficient sound projection.

This invention was designed to overcome the inherent disadvantages of hitherto known public address systems. In effect it uses or involves a small, light and attractive cabinet box having its own speakers, a built in microphone, amplifier circuit and power supply. The cabinet itself has in front an attractive speaker screen and is finished to appear as a decorative item of furniture. The microphone and its wire are designed to be held in a small compartment within the cabinet. A microphone stand is designed to fit into the same compartment in which the microphone is held and to pivot upwardly to hold the microphone when the voice projector is in use.

The back side of the box is provided with an off-on switch and with a volume control. No other control means are required. The top of the cabinet slopes downwardly toward its back end to present a convenient surface for holding notes, material to be read, and the like. The cabinet, of course, is designed to sit on a table or desk or its own stand. The microphone is at a convenient height with respect to the speakers face.

This portable lectern cabinet is so arranged that the microphone when in use is in the same general plane as 3,3 I 9,001 Patented May 9, 1967 the horn speaker cone in order that propagated and source sound are in phase. Additionally the horn is left open around its outside to form an acoustic resistance although it is contemplated that the space around the horn may be filled with foam rubber or foam plastic or cotton. Lastly the horn is constructed in strict conformance with formulae to produce the maximum performance which it is capable of realizing.

Accordingly, it is an object of this invention to provide a portable voice projector which is entirely self-contained.

Another object of this invention is to provide a portable voice projector which is very light and thus very easily transportable.

Yet another object of this invention is to supply a portable voice projector which with the exception of the microphone extension eliminates cords and wires running to electrical outlets and other pieces of equipment.

Another object of this invention is to furnish a portable voice projector which is simple in design, rugged in construction and economical to produce.

Still another object of this invention is to provide a portable voice projector which can be placed on a desk, a table or upon a stand of its own to present to the speaker a convenient reading surface.

A further object of this invention is to provide a portable voice projector which because of its design projects a true and undistorted amplification of the normal conversational tone of the speakers voice.

Yet a further object of this invention is to supply a portable voice projector which can be used in spacious auditoriums or within the confines of a conference room.

An even further object of this invention is to furnish a portable voice projector which because of its design eliminates the troublesome problem of feedback disturbances interfering with the voice projection.

A still further object of this invention is to provide a portable voice projector employing a microphone mounting which eliminates vibration, thus further reducing the possibility of feedback.

These, together with other objects and advantages which will become subseqently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings, forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

FIGURE 1 is a view in perspective of the invention showing it ready for use and showing some of the internal construction in dotted line to facilitate understanding;

FIGURE 2 is a top plan View with the top of the box cut away to show the ararngement of speakers, microphone and microphone mounting compartment, and amplifier and power supply locations;

FIGURE 3 is a partial view in perspective showing in greater detail the structure of the pivotal microphone mounting;

FIGURE 4 is a partial view in perspective showing the frame and screen which cover the open or speaker side of the cabinet;

FIGURE 5 is an alternative embodiment of a microphone mounting stand which may be employed in place of that one shown in FIGURE 3;

FIGURE 6 is a partial elevational view in section of the manner in which the tube of the mounting stand is attached to the mounting plate and the manner in which the plate itself is resiliently mounted;

FIGURE 7 is a cross section view through any two of the plate mounting screws and grommets; and

FIGURE 8 is a diagrammatic view of the horn showing the variable functions or quantities which enter into calculating the relative dimensions of the horn by use of formulae.

Referring now to FIGURES l and 2, it will be seen :hat the box or cabinet 18 is comprised of left side wall 11, right sidewall 12, a rear wall 14 and bottom wall 18. The front of the cabinet is in effect left open. However, when the speakers are placed within the cabinet they have attached thereto a speaker screen 16 which covers the forward opening in said cabinet. The forward end of the cabinet is of slightly higher dimension than the rear part. Thus, the top wall or reading surface 20 slopes slightly downwardly from front to back. However, there is no reason that the cabinet could not assume other shapes if it were so desired.

FIGURE 2 shows that along left wall 11 on the inside thereof there is constructed a narrow compartment generally designated by the number 22. Compartment 22 extends along most of the depth of side wall 11, perhaps three-quarters of the way from back to front and is just wide enough to accommodate the microphone and microphone stand and a length of microphone cord. Said compartment has side wall 24 and end wall 26. Both walls 24 and 26 extend from the bottom wall 18 to the top wall 20.

Directly across from compartment 22 near the inside surface of right wall 12 and near the back corner of the cabinet is an upright, rectangular box 28. Said box contains the battery dry cells which comprise the power supply for this invention. The batteries are inserted into box 28 by virtue of an opening (not shown) in the bottom wall 18 of said cabinet. A door is attached to said bottom wall for covering the opening and for holding the batteries firmly within box 28. Box 28 can be seen to extend upwardly from the bottom wall 18 to about half way to the top wall 20 and is positioned entirely in the back half of said cabinet. A circuit board is attached to right side wall 12 just above battery box 28 and has attached thereto all of the components and transistors forming the the amplifier 30, t

On the inside of the back of the cabinet are placed generally upright studs or braces 32 and 34. The rear inside corners of the cabinet are strengthened by generally upright corner braces 32. At somewhat less than half the distance from braces 32 to the center of back wall 14 are generally upright studs or braces 34. Said braces 34, besides strengthening the cabinet structure serve as means for holding the speaker assembly which is generally designated by the number 36 in a centered position within the cabinet.

The speaker assembly generally designated by number 36 is provided with box 38 which contains the large speaker cone 40. The rear of box 38 has resilient vibration and shock absorbing mounting strips 42 and 44 made of foam rubber or the like. As can be seen, said mountings 42 and 44 are adhered to the back of box 38 to space it from back wall 14 and from the upright braces 34. The front of box 38 is provided with a sound channeling or directing horn which is made of wood. The horn itself is comprised of flaring or curving side walls 48 and upper and lower walls 46. An opening is provided in the front space of box 38 in order to permit the sound from cone 40 to be projected out of cabinet The connection between the horn and box 38 is reinforced by upright reinforcing numbers 50 on the outside of the curved walls 48, and the front of box 38.

The speaker assembly 36 comprising both horn and speaker box 38 is constructed of wood. It can be seen that the horn flares outwardly from about the middle one-half of box 38, nearly to the front inside edge of the cabinet. A smaller treble speaker, sometimes called a tweeter, is installed within the interior of the horn. Small speaker 52 is such that it is centered in the forward half of the horn and in the upper part thereof by an appropriate mounting mechanism (not shown). Having both a "base speaker 40 and a treble speaker 52 gives truer voice projection. It is entirely possible that a second treble speaker could be placed within the horn, however, the

preferred embodiment contains only one such treble speaker.

The forward wall 16 of cabinet 10 as mentioned above is essentially a screen for the speakers to give the cabinet an attractive appearance from the front. FIGURE 4 shows that the forward wall 16 is a simple flat framework 54 having a decorative screen 56 placed on the outside thereof. Frame 54 is actually attached for assembly purposes to the upper and lower walls 46 of the horn of speaker assembly 36. Glued or otherwise attached to an interior vertical frame piece of frame 54 are upper brackets 60 and lower brackets 62. Said brackets 60 and 62 are essentially L-shaped with one arm thereof extending outwardly generally horizontally to overlie the exterior surfaces of both top and bottom horn walls 46. Brackets 60 and 62 are attached to said walls 46 by a screw or bolt or other appropriate detachable means. Thus, the frame and screen comprising wall 16 are not in actual practice attached to any part of the frame. Bolt means (not shown) which are inserted through bottom wall 18 of the cabinet are designed to hold the speaker assembly 36 within the cabinet. Upon removal of said bolt means, the entire speaker assembly 36 together with the forward wall 16 may be removed from the cabinet.

It will be understood that the horn or speaker assembly 36 is a single rigid structure which is supported at the back by box 38 and in the front by brackets 60 and 62. The horn proper, i.e. top and bottom horn walls 46 and curved side walls 48, does not contact the cabinet, except for bolt means (not shown) which extend through the bottom of the cabinet and attach to lower screen brackets 62.

Essentially the speaker assembly 36, including cone box 38, is constructed according to the following formulae:

d= Fr (II) V =2.5dA (2.5 is minimum value) (III) A =7A (limits are 5% to 8 times A (IV) V =42OO A As mentioned briefly above it has been found that the best acoustical resistance or entrapment is negative space surrounding the horn. However, foam rubber or plastic might as easily be used, though air space is considered and has been shown to be most effective.

As mentioned above, compartment 22 is designed to hold the microphone, microphone mounting and the microphone cord. In the very forward portion of compartment 22 is a small horizontal block 64 which abuts and is connected to forward compartment wall 26, compartment side wall 24 and cabinet side Wall 11. Said block 64 is located approximately one-quarter to one-third the distance down from the topmost edge of compartment 22. A hole 66 is cut in block 64 so that it is large enough to conveniently receive the microphone. A bag 68 of felt or other suitable soft material is attached to the under side of said block 64 and is, of course, approximately the length of the microphone. In this way, a holder is provided for the delicate and sensitive microphone when it is not in use.

Vt should be as small as practical unless a two-way or multiple speaker is used to cover the frequency range. Fe is thehfrequency of crossover from the low frequency horn in sue a case.

A microphone mounting is situated at the top rear of compartment 22. FIGURES 1 through 3 show that the microphone mounting mechanism pivots about a point attached to wall 24. The pivot base which is generally designated by the number 74 is comprised of a pivot Wall 80, a mounting wall 78 and a cover Wall 76. The walls 76, 78 and 80 are connected to each other in the manner of three sides of a cube. A pivot bolt 82 extends from the compartment side of pivot wall 80 through said wall 80 and through said compartment wall 24. Appropriate washer means are employed to give a stiff pivot to the entire base 74 as opposed to a loose pivot. It can be seen that when the pivot base 74 is pivoted down, as shown in FIGURE 2, the cover wall 76 is uppermost. Said cover wall 76 is, of course, added to cover the opening which would otherwise exist and is flush with top cabinet wall 20.

A hole 84 is cut in the mounting wall 78 to receive the microphone stand cylinder 86. Said cylinder or tube 86 has a relatively light gauge wall. It fits into hole 84 snugly and is held there by pin 88 extending from edge to edge in mounting wall 78 and extending directly through holes cut into tube 86. On this way tube 86 is firmly held in and on mounting wall 78. The inside of tube 86 is provided with a light, flexible and resilient vibration damping material such as foam rubber or the like. This resilient material, termed vibration cushion 90, occupies the interior of tube 86. Vibration cushion 90 is adhered to the interior surfaces of said tube 86 and has running down through the center thereof 3 circular passage 92 which receives the microphone shaft It can be seen that the microphone shaft 94 terminates above the pin 88. Said shaft 94 is also adhered to the vibration cushion 90 so as to give in effect a stationary but non-rigid mounting for the shaft. Atop shaft 94 is microphone swivel yoke or jaw 96 having the slot 97. Slot 97 accommodates a swivel arm 100 which turns tightly on a horizontal axis and which supports a collar 102. An appropriate pivot pin 98 extends between the jaw or yoke 96 through slot 97 and of course through the swivel arm 100. Collar 102 is designed to hold microphone 70, and the split in said collar, of course, is to permit insertion of said microphone in said collar without obstruction by cord 72.

An alternative microphone mounting assembly is shown in FIGURES 5 to 7. The three sided pivot base 74 is identical to that shown in FIGURE 3, having pivot wall 80, mounting wall 78 and cover wall 76. Similarly, bolt 82 extends through pivot wall 80 and compartment wall 24 to provide an appropriate pivot axis for base 74.

Mounting wall 78 is provided with a centrally located hole 110 through which microphone mounting tube 116 extends. On the underside of mounting wall 78 is located plate 114, having a threaded hole therein for threadably receiving the extreme lower end of tube 116. Plate 114 is isolated from direct contact with any portion of base 74 by virtue of a grommet and screw connection on each of the four corners of said plate. Said plate 114 has four holes 118 drilled therethrough into which is insereted a resilient grommet 120 made of rubber or plastic or the like. It will be seen that grommet 120 spaces and cushions plate 114 from wall 78 and that in addition it isolates washer 122 and wood screw 124 from contact with plate 114. In this manner plate 114 is resiliently mounted so as to be freeof vibration which might otherwise be conducted into the microphone to set up undesirable interference with sound projection.

Tube 116 is of smaller diameter than hole 110 in mounting wall 78 so that resilient annular cushion 112, which is made of foam rubber or the like, can be placed between the tube wall and the surface defining hole 110. Said cushion 112 is adhered to the edge of hole 112.

An inner extension tube 126 is telescopically received in mounting tube 116 in conventional manner. Locking collar or sleeve 128 tightens said extension tube 126 in the desired position. Extension shaft 126 has attached to the top thereof the microphone holding means shown in detail in FIGURE 3.

It will be appreciated from the above descriptive matter that three features of this invention contribute to is being superior to any other form of public address system now known.

By designing the speaker assembly according to the formulae shown above maximum output with minimum distortion of the sound is realized. Secondly an opening or space around the speaker assembly provides an acoustical entrapment for noises and vibrations which might otherwise interfere with sound projection. Thus, surrounding the speaker assembly to the extent possible with air space provides an acoustical resistance which greatly contributes to performance. As noted above the air space surrounding the speaker assembly may be substituted for with foam rubber or cotton fiber or some other type of acoustically resistant material. However, tests have shown that air space serves best. -It is important that this acoustical trap be provided between the microphone and the speaker assembly.

The third factor contributing to the remarkable qualities of this invention is the in phase operation of the microphone and the speaker cone. This feature requires that the microphone be mounted to one side in the general area defined by the generally vertical planes which pass through the forwardmost and rearmost points of the cone.

The three factors just mentioned when combined as indicated add up to as many as 10 decibels of increased output to the normal projected sound.

FIGURE 2 shows that when the lectern is not being used, the microphone can be taken from the mounting and placed in its holder. At the same time the empty microphone mounting assembly can be pivoted downwardly to lie entirely within compartment 22. Ample storage space is provided for a considerable length of microphone cord which can be coiled, and placed below the mounting assembly. Compartment 22 is covered by a door 104 which is hinged on one side thereof for convenient opening and closing. Back wall 14 of the cabinet is provided with a volume control 106 and an on-off switch 108.

The foregoing is considered as illustrative only of the principle of this invention. Since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

What is claimed is:

1. A self-contained sound projecting apparatus, comprising:

(a) a cabinet means having an open side therein;

(b) a speaker assembly means within said cabinet means for directing sound through and out of said open front side, said speaker assembly means including a sound projecting horn substantially isolated from contact with said cabinet means so as to pro vide air space between said horn and the inside surfaces of said cabinet means connected with the space without the open side of said cabinet, said air space forming an acoustical interruption and entrapment barrier substantially surrounding said horn to absorb a portion of the speaker output;

(c) microphone supporting means within said cabinet means located to one side of said speaker assembly means in an area generally bounded by the frontmost and rearmost lines of the speaker cone for said speaker assembly means to permit in phase operation of said microphone and speaker, said supporting means being mounted in a vibration proof means; and

(d) sound transmitting means within said cabinet means for connection with said speaker assembly means including a microphone, amplifier and power supply.

2. The self-contained sound projecting apparatus described in claim 1 wherein said microphone supporting means comprises a cylinder mounted with respect to said cabinet and having an interior provided with a light, flexible and resilient vibration damping material;

and a microphone shaft supported in a longitudinal bore through said resilient material.

3. The self-contained sound projecting apparatus described in claim 1 wherein said microphone supporting means comprises a plate resiliently mounted with respect to said cabinet, a tube attached to said plate and extending through a resilient annular cushion supported with respect to said cabinet, and a microphone shaft supported by said tube.

4. A sound projecting apparatus comprising a cabinet forming a generally enclosed structure having one side substantially open,

a sound reproducer having an open end, and

means for positioning said sound reproducer within said cabinet for forming an acoustical interruption and entrapment barrier to acoustic feedback to receive a portion of the sound reproducer output, said means locating the open end of said sound reproducer facing outwardly toward the open side of said cabinet and form-ing (i) a first substantially continuous air space between the open end of said sound reproducer and the inside surfaces of said cabinet and (ii) another open air space substantially surrounding the open end of saidsound reproducer and connecting said first air space with the space without the open side of said cabinet.

5. A sound projecting apparatus comprising a cabinet forming a generally enclosed structure having one side substantially open,

a sound reproducer having an open end, and

means for positioning said sound reproducer within said cabinet for forming an acoustical interruption and entrapment barrier to acoustic feedback to receive a portion of the sound reproducer output, said means locating said sound reproducer so that (i) the open end of said sound reproducer faces outwardly toward the open side of said cabinet forming a substantially continuous opening between the outer perimeter of the sound reproducer and the inner perimeter of the open side of said cabinet and (ii) the sound reproducer is substantially out of contact with said cabinet to form an air space between said sound reproducer and the inside surfaces of said cabinet.

6. The sound projecting apparatus described in claim 5 wherein said air space between said sound reproducer and the inside surfaces of said cabinet is filled with an acoustically resistant material such as foam rubber, foam plastic, or cotton fibre.

7. The sound projecting apparatus described in claim 5 wherein said sound reproducer includes a speaker cone at its extreme rearward end opposite the open end of said sound reproducer, and an enclosure within the air space between said sound reproducer and the inside surfaces of said cabinet for substantially confining said speaker cone, the walls of said enclosure being interposed between said speaker cone and said air space.

References Cited by the Examiner UNITED STATES PATENTS 1,319,774 10/1919 Kallajian 179-147 1,566,212 12/1925 Hoban 179146 X 2,063,224 12/1936 Bowles 1791 2,768,702 10/1956 Lowry 17931.1 2,797,766 7/1957 Sullivan 18131.1 2,830,118 4/1958 Kohler 1791 2,868,878 1/1959 Pronio 179--1 3,023,274 2/1962 Shaw 179-1 3,115,548 12/1963 Stowell 1791 3,153,123 10/1964 Harman 179-448 OTHER REFERENCES Hi Fi Loudspeakers & Enclosures, A. B. Cohen, John F. Rider Publisher, Inc., New York, N.Y., Copyright 1956, pages 217229 relied on.

KATHLEEN H. CLAFFY, Primary Examiner.

WILLIAM C. COOPER, ROBERT H. ROSE, Examiners.

A. J. SANTORELLI, R. MURRAY, Assistant Examiners. 

1. A SELF-CONTAINED SOUND PROJECTING APPARATUS, COMPRISING: (A) A CABINET MEANS HAVING AN OPEN SIDE THEREIN; (B) A SPEAKER ASSEMBLY MEANS WITHIN SAID CABINET MEANS FOR DIRECTING SOUND THROUGH AND OUT OF SAID OPEN FRONT SIDE, SAID SPEAKER ASSEMBLY MEANS INCLUDING A SOUND PROJECTING HORN SUBSTANTIALLY ISOLATED FROM CONTACT WITH SAID CABINET MEANS SO AS TO PROVIDE AIR SPACE BETWEEN SAID HORN AND THE INSIDE SURFACES OF SAID CABINET MEANS CONNECTED WITH THE SPACE WITHOUT THE OPEN SIDE OF SAID CABINET, SAID AIR SPACE FORMING AN ACOUSTICAL INTERRUPTION AND ENTRAPMENT BARRIER SUBSTANTIALLY SURROUNDING SAID HORN TO ABSORB A PORTION OF THE SPEAKER OUTPUT; (C) MICROPHONE SUPPORTING MEANS WITHIN SAID CABINET MEANS LOCATED TO ONE SIDE SPEAKER ASSEMBLY MEANS IN AN AREA GENERALLY BOUNDED BY THE FRONTMOST AND REARMOST LINES OF THE SPEAKER CONE FOR SAID SPEAKER ASSEMBLY MEANS TO PERMIT IN PHASE OPERATION OF SAID MICROPHONE AND SPEKER, SAID SUPPORTING MEANS BEING MOUNTED IN A VIBRATION PROOF MEANS; AND (D) SOUND TRANSMITTING MEANS WITHIN SAID CABINET MEANS FOR CONNECTION WITH SAID SPEAKER ASSEMBLY MEANS INCLUDING A MICROPHONE, AMPLIFIER AND POWER SUPPLY. 